The compliments come not just because the car has such classic sophisticated lines, but are a reflection of how the owner keeps it. The compliment is directed at you even more than the car. It comes as recognition for your hard work AND good taste.

I had a red Cavalier coupe that got adoring glances, not because it was an exotic but as recognition of how it was kept. Be proud to own such a fine car, keep it clean and show your pride of ownership. As FP said a polite and humble "thank you" is most appropriate.